The overall objective of this proposal is to further elucidate the physiological importance of the interferon-inducible, dsRNA-dependent protein kinase, PKR, in the cell. Evidence suggests that this kinase plays a crucial role in IFN's response to viral infection, tumorigenesis, and may function as a signal transducer involved in the regulation of dsRNA-activated growth control genes such as NF-kB and c-myc. In this proposal, the P.I. will attempt to further understand the functions of PKR in vitro, using inducible cell-lines and in vivo, using genetically engineered animal models that lack or overexpress this gene. Accordingly, the following specific aims will be pursued: 1) Analysis of the mechanisms of PKR's growth suppressive phenotype using inducible-cell lines that have recently been developed. Previously, all attempts to express this kinase in eukaryotic cells have failed. Moreover, using these cells, the P.I. will start to address the mechanisms of mutant PKR-induced malignant transformation. 2) Characterization of mice that lack PKR following gene targeting in embryonic stem-cells. These studies will include examining whether the control of cellular growth in these mice has been impaired. Importantly, the P.I. will examine whether PKR null mice or cells derived from the mice are predisposed toward tumorigenesis. 3) The P.I. has developed transgenic murine lineages that overexpress wild-type PKR or trans-dominant mutant PKR variants. These mice will be compared to the in vitro cell-line studies and to the PKR null lineage models. These studies are expected to contribute toward 1) elucidating the physiological properties of PKR, including importance in the regulation of growth control and tumor suppression, 2) understanding the mechanisms of IFN-mediated functions in the cells, and 3) furthering our scant knowledge of the importance of translational control in tumorigenesis.